Post-Quantum Cryptography, Demystified. Part 1

TL;DR

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Cryptographically Relevant Quantum Computers, or CRQCs, are on the horizon. When they arrive, they will threaten many of the public-key cryptography algorithms that secure today’s digital world.

The time has come to prepare.

Organizations need to enable their teams, ask better vendor questions, inventory their cryptographic ecosystem, prioritize the highest-risk systems, create a course of action, execute migrations, automate certificate and key lifecycle management, and build crypto agility so they can transition from classical cryptography to quantum-resistant cryptography without treating every future algorithm change like a once-in-a-generation fire drill.

Q-Day

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Quantum computers; It sounds like science fiction, but the security threat they create is very real.

The concern is not that every quantum computer will magically break every encryption system. The concern is that a sufficiently powerful quantum computer, often called a Cryptographically Relevant Quantum Computer, could break many of the public-key cryptographic algorithms that modern systems depend on.

ℹ️ Cryptographically Relevant Quantum Computer (CRQC)

A CRQC is a quantum computer powerful enough to attack real-world cryptographic systems that would be infeasible to break with classical computers. This term distinguishes abstract physics experiments from machines that present an actual security risk

Even though at its most basic level we are just talking about math, the math that today serves as the foundation for cryptography is at risk. This is because the math that is securing our resources today is essentially too hard for classical computers to reverse engineer in a realistic timeframe. More specifically there are still challenges with current classical computers and solving math problems such as prime number factorization.

This matters because much of today’s digital trust depends on math, but these math problems are difficult for classical computers to solve in a realistic timeframe. RSA, for example, relies on the difficulty of factoring very large numbers. Even elliptic curve cryptography (ECC) relies on similar but different math, but the theme is the same: these systems are secure because the reverse math operation is computationally impractical for classical machines.

A CRQC changes that assumption. e.g Shor’s Algorithm.

Granted this does not mean symmetric encryption such as AES instantly becomes useless, and it does not mean every security control fails at the same time. But it does mean many of the mechanisms we use for key exchange, digital signatures, identity, certificates, firmware validation, and secure communications will need to evolve.

That evolution is Post-Quantum Cryptography.

ℹ️ Post-Quantum Cryptography (PQC)

PQC refers to cryptographic algorithms designed to resist attacks from both classical computers and quantum computers.

Why This Matters

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The cryptography we have relied on for decades has secured emails, banking systems, cloud services, military communications and more. Throughout this time, the practical assumption was simple: if you used modern algorithms correctly, with appropriate key sizes, attackers could not realistically break the cryptography with classical computing power.

A CRQC changes the risk model.

A classical computer may require an unrealistic amount of time to break certain cryptography but a sufficiently capable quantum computer could theoretically solve some of those cryptography math problems dramatically faster. Creating cryptography that is resistant to CRQCs is the goal of Post Quantum Cryptography (PQC). This is why the industry is moving toward quantum-resistant algorithms such as ML-KEM for key establishment and ML-DSA or SLH-DSA for digital signatures.

ℹ️ Quantum computers & quantum mechanics

A CRQC uses quantum mechanics to essentially “cheat” and solve the hard math problems that classical computers struggle with.

The Mental Model

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Quantum computing is to classical computing what the internet was to postal mail.

The internet did not make postal mail disappear. It changed the assumptions around speed, scale, and even organizational designs. Quantum computing will not make classical computing disappear. You probably will not use a quantum computer to send an email, write a document, or browse the web. Classical and quantum systems will likely exist together but the existence of quantum computing changes the assumptions that classical cryptography depends on.

This is the shift. PQC is not about replacing every computer with a quantum computer. It is about replacing vulnerable cryptographic assumptions before they become enterprise-wide liabilities.

What you need to know

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When people talk about PQC, the conversation often becomes overly focused on the non-existent viable quantum computer or that vendors will all just deal with the PQC problem. That is understandable, but incomplete.

The risks are already here.

1. Harvest Now, Decrypt Later

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The most immediate concern is Harvest Now, Decrypt Later (HNDL). Look up wifi sniffing if you want to feel naked at home.

An attacker does not need a CRQC today to create future damage. They can collect encrypted traffic or sensitive encrypted data now and store it until quantum capabilities mature. If the data still has value in five, ten, fifteen, or twenty years, then the organization has a current risk even if the decryption event happens later.

This matters for industries with long-lived sensitive data: healthcare, defense, financial services, government, critical infrastructure, intellectual property, legal records, really anything involving national security or personal privacy.

The question is not simply, “Can someone decrypt my data today?” The real question is, “Will my data still matter when quantum decryption becomes practical?”

2. Architecture Risk

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PQC is not as simple as swapping algorithms. Post-quantum algorithms can have different key sizes, signature sizes, performance characteristics, protocol & certificate implications, and hardware constraints. Larger signatures can impact certificate chains, size constrained devices, network protocols, TLS handshakes, firmware signing workflows, HSM integrations, smart cards, and legacy applications.

The PQC risk is operational, performance-related, and dependency-driven. You need to know where cryptography is used before you can know what will break. Check out Cryptography Bill of Materials (CBOM)

3. Operational Risk

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Classical cryptography is already difficult to manage well. Entire companies exist because certificate lifecycle management, PKI operations, key rotation, secrets management, HSM operations, and cryptographic policy enforcement are hard. PQC adds another layer of complexity to a field that many organizations already struggle to operationalize.

Par for the course, the biggest risk may not be the technology. The biggest risk may be the organization’s inability to change. People, process, and technology all matter here.

If security teams understand PQC but application teams do not, migration and adoption stalls. If enterprise architects understand the risk mitigations but procurement teams do not ask the right vendor questions, risk gets reintroduced through new purchases. If platform teams automate certificates but no one owns cryptographic inventory, teams end up modernizing blindly.

PQC is not just a security project. It is an enterprise initiative.

Current Timeline - June 2026

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The US executive branch has issued a federal mandate in November 2022 to “prioritize the timely and equitable transition of cryptographic systems to quantum-resistant cryptography, with the goal of mitigating as much of the quantum risk as is feasible by 2035.”

Then NIST finalized the first three post-quantum cryptography standards in August 2024; FIPS 203, 204, 205.

In May 2026, Google released their updated timeline regarding PQC to 2029. US Federal guidance has been pushing agencies to inventory cryptographic systems, especially high-value assets and high-impact systems. CISA and the NIST National Cybersecurity Center of Excellence have focused on providing information on awareness, preparation, discovery and inventory, risk assessment and planning, migration execution, validation and monitoring in order to mitigate the risks of a CRQC coming before we are ready. See NIST CCOE FAQ

The market is also waking up. Government RFIs, vendor roadmaps, hyperscaler experimentation, and major quantum investments are all signals that this is becoming a procurement, compliance, and architecture conversation.

Takeaway

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Post Quantum Cryptography is not simply about mitigating Q Day, but about building a strong foundation through visibility, automation, and enabling crypto agility to adapt with the next generation of quantum computers. To learn more about how to mitigate these risks, check out Part 2 where we dive into more of the implementation, cost, and impact on becoming PQC ready.

Acronyms and Definitions

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